More Friction Over Merits Of Antilock Brake Systems

ANTILOCK brakes were supposed to be the savior of automotive safety - the seatbelts of the '90s. Even more than airbags, the technology allowing cars to stop quickly without locking the wheels enjoyed across-the-board support from automakers, government safety experts, and consumers.

But a funny thing happened on the way to the stop sign. Suddenly, a new debate is breaking out over how effective the ''revolutionary'' technology really is.

The industry is trying to refute a government study that came out last year showing that antilock brake system (ABS) aren't as terrific as originally thought - and thus there is no need for a federal regulation requiring them on all new vehicles.

The debate is not an idle one. Car manufacturers have invested millions of dollars in developing the new braking systems, and are interested in getting a return on their money. Moreover, many insurance companies offer discounts to consumers who have vehicles equipped with the technology. Will insurers now balk at offering lower rates?

One company already has. In light of the government findings the United Services Automobile Association has canceled the discounts.

Bob Knoll, director of auto testing for Consumer Reports, is ''concerned'' that the publicity surrounding the government findings ''will convince people that antilock brakes aren't needed.'' ''We've tried them in a huge number of cars in a wide variety of conditions, and they've worked as advertised,'' he says.

Last week, an auto-industry association defended the safety gains in a new report stating that antilock brakes reduce the number of traffic accidents by 9 percent to 10 percent. That represents a reduction of 500,000 car accidents a year, according to the American Automobile Manufacturers Association (AAMA), a lobbying group for US carmakers, which commissioned the study.

While both the government and the auto-industry study showed a decrease in many types of accidents especially on wet or snow-covered roads, the government study mysteriously reported a 20 percent increase in single-car ''run-off-road'' accidents and a corresponding 28 percent rise in rollovers.

''What we're trying to find out is why,'' says Barry Felrice, of the National Highway Transportation Safety Administration (NHTSA), which conducted the study. A number of possible explanations have emerged:

Drivers have been taught to pump the brakes, rather than stand on them, in panic stops, effectively turning the antilock mechanism on and off and reducing its effectiveness.

Drivers who are not used to antilock brakes are startled when the brake pedal starts vibrating underfoot and rattling like a drumstick running down a washboard - indications that the antilock mechanism has gone into action. So they lift off the brakes, again reducing braking power.

Or drivers get over-confident, thinking that their antilock brakes will stop them faster than conventional brakes. They simply drive too fast, and no amount of braking will keep them on the road.

Antilock braking systems use a tiny computer to monitor each wheel and sense when it is about to lock up. The computer then eases off the pressure on the individual brake, rather than make the driver release the pressure on all the wheels to avoid lockup.

ABS was not designed to reduce stopping distances, but rather to allow drivers to maintain steering control in difficult stopping situations, such as when some of a car's wheels are on ice or gravel and others are not. Antilock brakes reduce the incidence of spin-outs, and cars using them ''don't run into things as much,'' Mr. Felrice says.

''We have total confidence in the technology,'' Felrice says, adding that manufacturers, dealers, suppliers, and the government all need to start teaching drivers about antilock brake capabilities.

But while it stands behind the technology, the NHTSA decided last March to abandon an antilock brake mandate. After its study, the agency just didn't have the data to support a mandate.

''If we had mandated ABS, it would have been the most expensive regulation in NHTSA history,'' he says. The cost per vehicle of installing antilock brakes is more than $400.